The purpose of the proposed research is to provide correlational data relevant to understanding the origins of sex differences in spatial ability which seem to arise, or at least increase in size, at the onset of adolescence. Waber (1976, 1977b) has proposed that higher spatial ability is related to later onset of puberty. Her hypothesized mechanism is that ongoing brain lateralization is curtailed by puberty, with greater lateralization related to higher spatial ability. An alternate causal path is through the influence time of maturation is known to have on personality and interests. In the present research, pubertal development will be measured in a sample of 160 seventh graders and eighth-graders using Tanner's (1962) rating scales. Participants will be given two tests of spatial ability. They will complete several measures of personality and sex-role orientation: five scales from the California Psychological Inventory, the Bem Sex-Role Inventory, and actual self- and ideal self-ratings on ten intellectually relevant but sex-stereotyped characteristics identified by Nash (1975) as correlated with spatial ability. Finally, ratings will be made of involvement in a list of adolescent hobbies and activities to be developed for this study. (Undergraduates will be asked to rate the degree to which these activities require spatial ability, the degree to which they are sex-typed at adolescence, and the degree to which they would enhance adolescent social prestige.) These data will allow several analyses. First, it will be possible to attempt to replicate several sets of data: Waber's findings (which did not replicate in Petersen's (1976) reanalysis of Fels data), relationships of time of maturation to personality (still somewhat unclear for females) and relationships of spatial ability to personality (still somewhat unclear for males). Secondly, path analysis will be utilized to contrast the hypothesis that time of maturation affects spatial ability indirectly, through effects on personality and interests, with the hypothesis that the link does not involve such social mediation.